Ubiquitin-Proteasome Pathway System (UPS) is a critical pathway that regulates key regulator proteins and degrades misfolded or abnormal proteins. UPS is central to multiple cellular processes, and if defective or imbalanced, it leads to pathogenesis of a variety of diseases. Posttranslational modification of proteins by ubiquitin is a fundamental cellular mechanism that regulates protein stability and activity and underlies a multitude of functions, from almost every aspect of biology. The covalent attachment of ubiquitin to specific protein substrates is achieved through the action of E3 ubiquitin ligases. These ligases comprise over 500 different proteins and are categorized into multiple classes defined by the structural element of their E3 functional activity. Specifically, both HECT and RING ligases transfer an activated ubiquitin from a thioester to the e-amino acid group of a lysine residue on a substrate; however, HECT ligases have an active site cysteine that forms an intermediate thioester bond with ubiquitin, while RING ligases function as a scaffold to allow direct ubiquitin transfer from the E2 to substrate. Recent evidence suggests that a subfamily of RING ligases, the RING-between-RING (RBR) family, may contain a catalytic cysteine residue 1,2 in addition to a canonical RING domain. (Riley et al. 2013. Nat Commun. 4:1982, “Riley et al.”), which is herein incorporated by reference in its entirety.
Deubiquitinating proteins and ubiquitin-specific proteases (DUBs and USPs) and E3 Ligases play a vital role in the UPS. These proteins are supported by flexible Zinc Finger (ZnF) domains which stabilize the binding of ubiquitin (Ub) for specialized functions.
Parkin is a RING-between-RING E3 ligase that functions in the covalent attachment of ubiquitin to specific substrates, and mutations in Parkin are linked to Parkinson's disease, cancer and mycobacterial infection. The individual RING domains for Parkin have been the subject of much debate, in regards to the specific residues that coordinate Zn ions, as well as their relationship to canonical RING crossbrace structures defining classical E2-binding domains. R0 is a novel domain structure, but is more similar to Zn-finger domains than to E3 RING domains (Riley et al. 2013. Nat Commun. 4:1982)
While many drug discovery programs focus on the UPS, few have been successful due to the lack of selectivity and direct access to enzymatic protein active sites. The present invention is directed towards a novel approach of disrupting Zn-finger domains that provide a therapeutic benefit for various diseases and disorders, including oncology and neurology disorders.